Since you live in the UK our health care is going to be different in regards to seeing a dentist. Which makes what I may suggest for you not applicable. I too say at this point changing dentist may be a good idea since your teeth and gum pain has not been resolved with the current dentist you are seeing.
If I have to go back more the twice for the same issue I am going to go some where else to get matter taken care of.
I did however find a web site that gives very good information on gingivitis. I think that may help you understand what you may have.
Note: I am only listing the site for the information they give on gingivitis not the product that they are in the end trying to sell.
Hope this helps you.